Conventional automation control and data acquisition systems typically include one or more sensing or control devices that are capable of controlling or obtaining signal measurements from equipment to which they are connected. The sensing and control devices operate under the control of one or more processing units. As an example, a conventional automated data acquisition and control system can be used to control the precise operation of machinery such as that used in the process of semiconductor fabrication.
Continuing the example of fabricating semiconductor devices, such a process involves accurately controlling a complex arrangement of heating and cooling machinery, semiconductor wafer conveyance systems and chemical vapor deposition system hardware (valves, gas and pressure measurement devices, thermocouples, and the like). Each element of the semiconductor fabrication system (i.e., each temperature sensing device, valve, mechanical manipulator, pressure sensor, thermocouple, etc.) can include an attached sensing and/or control device that is capable reading and writing data (e.g., analog and/or digital control signals) to and from that element. The control devices are coupled to a central processing unit that orchestrates their operation in a prescribed sequence. The central processing unit thus precisely controls the operation of the various elements in the system to allow the elements to work together in a prescribed manner for fabrication of semiconductor devices. Semiconductor fabrication is only one example of a typical use for an automation control and data acquisition system.
Within a conventional data acquisition system, the processing units are typically coupled to the sensing and control devices by standardized networking cables such as category-five (CAT 5) networking cables or other wires, lines, data links or the like. In such systems, the central processing unit exchanges data with the sensing and control devices using a standardized network protocol such as the Transmission Control Protocol (TCP) and Internet Protocol (IP) or TCP/IP. TCP/IP provides a reliable mechanism to exchange packets of data between the processing unit and control devices without having to worry about loss of data packets or networking transmission errors.
Typical conventional data acquisition systems can operate the TCP/IP protocol over an Ethernet network medium that utilizes, for example, standard 100-Base-T Ethernet hardware controllers within the communication ports of the central processing unit and the sensing and control devices. Such standardized Ethernet hardware operates a carrier sense multiple access with collision detection (CSMA/CD) protocol in order to detect packet transmission collisions within the network medium between devices. Using this protocol, when a network device is transmitting onto network medium, the Ethernet hardware continues to listen to the network. If another node tries to transmit at the same time, then the CSMA hardware detects a collision. The CSMA hardware then considers both transmissions from both network nodes to be corrupted and this protocol deletes any data received by recipient devices from the receiving queue that stores incoming packets. After collision detection, both network nodes wait a random period of time before attempting to again retransmit the same packets. Thus, CSMA/CD is stochastic in its nature. In addition, this protocol avoids upper layer protocols such as TCP/IP from having to be concerned with situations in which two or more devices attempt to transmit onto a network medium at one time. Other conventional protocols such as carrier sense multiple access with collision avoidance (CSMA/CA) operate in a similar manner but decrease the number of potential collisions.